In the field of wireless communication devices, significant efforts are being made to use digital signal processing techniques to perform many of the signal processing tasks more commonly performed with analog circuitry. For example, it is desirable to convert an analog signal derived from a received radio frequency (RF) signal to a digital signal so that subsequent filtering and demodulating tasks can be performed digitally.
A data converter device called a "sigma delta" data converter is useful in converting an analog signal to a digital signal, and vice versa. The sigma delta data converter consists of one or more integrators. Prior art continuous time sigma delta data converters have integrator signal swings that are a direct function of the input signal level. This can cause problems particularly when the sigma delta data converter is implemented with a basic complementary metal-oxide semiconductor (CMOS) process, often a preferred implementation to meet integration requirements. Simple CMOS processes do not typically provide capacitors that remain linear over the integrator signal swing variations imposed on the data converter. Double poly capacitors can be used in their place, but this increases the costs and inhibits comprehensive integration.
A data converter is needed which can be implemented in such a manner to allow for complete integration with other circuit functionalities using conventional semiconductor processes without degrading the performance characteristics causes by anticipated integrator signal swing.